Noun1. a legislative act finding a person guilty of treason or felony without a trial; "bills of attainder are prohibited by the Constitution of the United States" (hypernym) bill, measure (classification) law, jurisprudence

A bill of attainder (also known as an act of attainder or writ of attainder or bill of pains and penalties) is an act of a legislature declaring a person or group of persons guilty of some crime and punishing them, often without a trial. As with attainder resulting from the normal judicial process, the effect of such a bill is to nullify the targeted person's civil rights, most notably the right to own property (and thus pass it on to heirs), the right to a title of nobility, and, in at least the original usage, the right to life itself. Bills of attainder were passed in England between about 1300 and 1800 and resulted in the executions of a number of notable historical figures.

An act of the legislature by which one or more persons are declared to be attainted, and their property confiscated.

The Constitution of the United States declares that no state shall pass any bill of attainder.

During the revolutionary war bills of attainder and ex post facto acts of confiscation were passed to a wide extent. The evils resulting from them, in times of more cool reflection, were discovered to have far outweighed any imagined good.